The invention relates to a remote emissions sensing system and method that uses a composite detector beam of infrared (IR) and ultraviolet (UV) radiation. The detector beam is used to perform spectroscopic measurements upon an emissions source and the beam is not split during detection.
Remote emissions sensing systems generally are known. One such system comprises a source of electromagnetic radiation arranged to pass a beam of radiation through the exhaust plume of a motor vehicle as the motor vehicle passes by the system, and one or more detectors arranged to receive the radiation after it passes through the exhaust plume of the vehicle. Filters may be associated with one or more detectors to detect the intensity of electromagnetic radiation at a particular wavelength or range of wavelengths. The wavelengths may be selected to correspond to wavelengths absorbed by molecular species of interest in an exhaust plume (e.g., HC, CO, CO2, NOx, or other molecular species). The detector""s output voltage represents the intensity of the electromagnetic radiation measured by that detector. The voltages are input to a processor. The processor calculates the difference between the known intensity of the electromagnetic radiation source and the intensity detected by the detectors to determine the amount of absorption by particular molecular species (based on predetermined wavelengths with that species). Based on the measured absorption(s), the concentration of one or more molecular species in the emissions may be determined in a known manner. Such systems generally take a plurality of measurements (e.g., 50) over a predetermined period of time (e.g., 0.5 seconds). These measurements are then plotted and analyzed to determine concentrations of target emissions. When using a plurality of measurements, however, if one or more measurements are inaccurate, concentration calculations may be erroneous or invalid. For various reasons, inaccuracies can occur when remotely sensing emissions.
Some remote emission sensing systems do not have the capability to detect nitrous oxides (NOx). Other systems detect NOx with a UV beam and other molecular species with an IR beam. In one such system, the UV and IR beams are split into separate beams at the detector module. One reason for this splitting is that unequal detection times have been believed necessary for the UV and IR portions of the beam. For example, a longer UV detection time has been believed necessary to ensure adequate NOx detector signal. One problem with such a system is that unequal detection times require additional system elements which increase the difficulty in aligning the system. Other drawbacks exist.
One object of the invention is to overcome these and other drawbacks of existing systems.
Another object of the invention is to provide a remote emissions sensing system and method with a composite beam of IR and UV radiation that detects NOx and at least one other molecular species, where the alignment of the system is relatively easier than the alignment of a system wherein the UV and IR beams are split for detection.
Another object of the invention is to provide a remote emissions sensing system and method with a composite beam of IR and UV radiation that is not split for detection.
Another object of the invention is to provide a remote emissions sensing system and method with a composite beam of IR and UV radiation that detects NOx and at least one other molecular species, where the composite beam is alternately incident upon a NOx detector and a detector for the at least one other molecular species.